KDE GUI Login Configuration HOWTO

This is the KDE GUI Login Configuration HOWTO, a tutorial on customizing the GUI login screen. Topics include:
How to add other window managers to the drop-down selection list;
how to enable user selection icons in the login window;
and requiring root permission for system shutdown.

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This info is based on my RedHat 6.1 default KDE Workstation installation. If you are using
another distribution, or even another version of RedHat, or a different Workstation install,
then you may have to do some detective work. Hopefully, this info will give you what you need
to start detecting! This HOWTO began as the result of wondering how to add another window manager
or desktop environment to the drop-down list on the GUI login screen; further investigation
revealed other configuration options.

I began my own "detective work" when I found a reference on a RedHat List which
mentioned /etc/inittab, and its role in system startup. In
/etc/inittab I found the following entries, which define how the
X Window System is started in my distribution and version:

# Run xdm in runlevel 5
# xdm is now a separate service
x:5:respawn:/etc/X11/prefdm -nodaemon

No changes to prefdm are necessary; it determines which display manager is the
system default, and which runs the GUI login. During boot-up, prefdm parses
/etc/sysconfig/desktop and selects the display manager listed there;
in the case of my KDE Workstation install, this is kdm (KDE Display Manager).
Note that gdm (Gnome Display Manager) is not installed on my system; xdm (X
Display Manager) is installed by default as part of the X Window System, and
was apparently used by older versions of Red Hat.

WARNING: The procedures explained in this HOWTO involve making changes to system
configuration files; if you are not experienced in making such changes, some
caution is required. Introducing errors into such files may make your system
unstable, or cause it to crash. The procedures explained in this HOWTO have
been tested and should not cause problems if used correctly.

If you have KDE 2.2 or higher, and you are not comfortable with manual editing of system files, you may open a
terminal window (xterm or konsole) from your user desktop (NOT the root
desktop), then type and enter:

su -c 'kcontrol'

Enter your root password at the prompt, and make the changes from within the
KDE Control Center that appears: go to Applications ==> Login Manager. Choose
the appropriate configuration tab; you can easily configure every aspect of
the login screen from there. In Earlier versions of KDE, kcontrol can modify
kdmrc, but cannot modify Xsession which is used in those versions; see the
note below about changes from KDE 2.2 and higher.

To see how to manually configure some of these, and see what these
configuration files do, proceed as follows:

(Caution: Some configuration files have changed since the version of kdm
I'm using, particularly since KDE > 2.0:

Much of the material in this new handbook applies to the older versions;
new features are also described therein.

Check the documentation for your version to identify the current configuration
files if you want to manually edit these, or just want to see how they work.

Do not use a word-processor program for editing system configuration
files; such programs introduce special formatting characters which will corrupt the files.
Use a text-editor, particularly one which can handle long lines without introducing
extra carriage-return or line feed characters into existing code. Suitable editors include
vim (vi improved), vi, and emacs. There are others, but these are usually installed by default
in Linux workstation installations; they each have features which make them especially suitable for
writing and editing computer code. See the bibliography section at the end of this HOWTO for
more information.

IMPORTANT: Before making changes to any system configuration files, you should make
back-up copies of the originals, so you can restore them in case of serious errors!

The files which we will be changing here are /usr/share/config/kdmrc, which
is where we add selection labels to the drop-down list on the login screen, and
/etc/X11/xdm/Xsession, which is where we add the path to the executables
for our labels (if you are using a different distribution, the path to these
files may be different; just do "locate kdmrc" and "locate Xsession"
in the shell [i.e., in a terminal emulation, such as xterm, or KDE's konsole]
to find them).

The default line to change in kdmrc looks like this:

SessionTypes=kde;gnome;anotherlevel;default;failsafe;

After adding selection labels for two new window managers, windowmaker and blackbox, the line looks like this:

Notice the positions where I have added the labels for the new window managers; all
entries will appear on the drop-down list in the same order as they
appear in the SessionTypes list. Next, the actual choosing takes place in
/etc/X11/xdm/Xsession. Here is what the appropriate section of
Xsession looks like before adding the new entries:

Here is what this section of the Xsession file looks like after adding the new
entries (NOTE that the selection labels must be exactly the
same in Xsession and prefdm, i.e., spelling and case must be identical):

Note that when the executables are installed in one of the paths shown below, only the
executable name is required after "exec"; otherwise the full path must be included,
as shown for "Xclients.anotherlevel" (above):

/usr/bin/

/usr/local/bin/

/usr/X11R6/bin/

/usr/bin/X11/

These examples should be enough for you to add your favorite window manager(s) to the
KDE graphical login, or to give you a starting point to find out how it's done in your
particular installation.

In RedHat 6.1, the default KDE login window shows a dialog box with a space to
type in the user name, one in which to type the user password, and a drop down
list to select the window manager/desktop environment of choice. By making the
following changes to /usr/share/config/kdmrc, user icons will appear in
the top of the login box.
Here is what the default lines that control user icon view in kdmrc look like (other
lines between these two are not shown, and are represented by "..."):

#Users=root;johndoe
...
UserView=false

Here are the same lines after editing; delete the comment character ("#") in
front of "Users=..." and change "johndoe" to your username (if there are more
user accounts on your system, you may add their usernames here, separated by semi-colons
as shown). Change "UserView=false" to "UserView=true" as shown here:

Users=root;johnpipe
...
UserView=true

Now, when you login, you may click on an icon with the mouse to enter the user name; you must still type in your password.

You can add your own icons in place of the default icons; place you own icons
in /usr/share/apps/kdm/pics/users/. They should be of size 64 x 64, according
to the kdm handbook; in KDE 1.x, the default icons are 62 x 63, and my new user icon is 60
x 60, so if icons are reasonably close to the specified 64 x 64 size, they
will work OK. The handbook says "kdm is able to handle icons of different
sizes, but the result looks messy.", so there is evidently some leeway here.
Your icons should be named 'username.xpm', for example my username is
"johnpipe" and my new icon is named 'johnpipe.xpm'

NOTE: at some time since kde 1.x, the icon format has been changed from '.xpm'
(XPixMap) to '.png' (portable network graphic).